Within countries of the world with sophisticated and well-developed medical care systems and facilities, there remain substantial portions of the population that do not access the medical care system. Those who fail to obtain medical diagnoses may represent up to 50% of those at risk for some medical conditions. This failure to access medical diagnosis and care may be due to fear, mistrust, restricted availability, or lack of information or finances. Undiagnosed and untreated individuals serve as a reservoir for increased spread of infection. In the past year, new AIDS cases in San Francisco have doubled to 900 (Investors Business Daily, page A2, Jul. 3, 2000) marking what many doctors fear is a breakdown of our current approach to controlling the infection.
In countries with less developed medical care systems and sophisticated diagnostic testing laboratories, most of the population may not receive prompt diagnosis of potentially treatable conditions. Illnesses such as AIDS, tuberculosis, malaria, and other infectious diseases may drain the country's talent and economic resources to the extreme, with an overall reduction in the standard of living and gross domestic product. (Confronting AIDS, Public Priorities in a Global Epidemic, World Bank Research Report, 1997). In sub-Saharan Africa, more than 10% of the population aged 15-49 carries HIV. In seven of the sixteen countries 20% are infected and in one country, Botswana, one in every three adults carries HIV (Investors Business Daily, page A1, Jun. 28, 2000, Global View of HIV Infection). This toll of medical illness stands as a barrier to becoming part of the community of twenty-first century planet earth with all of its benefits in education, communication and information exchange. These countries risk being hopelessly mired in sickness, death, and economic instability, without the help of more developed countries and new methods of diagnosis, treatment and prevention of disease.
Inexpensive, widely available and easily performed diagnostic tests that could be used by individuals anywhere and at any time, without the need of instrumentation or formal training, would contribute to earlier diagnosis of medical conditions for which the tests were available. These tests would also facilitate improved education regarding those medical conditions being detected by empowering individuals to become involved in their early detection and treatment. Earlier detection and improved education would be expected to result in reduced transmission of those infections for which tests were available to individuals, with the result of benefiting the entire society in terms of fewer infections, and increased health and workforce productivity. Researchers at the Centers for Disease Control in Atlanta, Ga., have used mathematical models to predict that availability of rapid tests for HIV would lead to testing of at least an additional 700,000 people, and detect more than 8,000 additional infected individuals (Los Angeles Times, page A10, Jun. 14, 2000, FDA Blamed for Holding Up Rapid AIDS Tests).
The major technological impediment to development of diagnostic tests suitable for use by individuals has been the lack of device formats that are both accurate and user-friendly for individuals. Accurate test methods have been available for many years but most have required instrumentation. A test that requires instrumentation does not fulfill the needs of individuals who do not choose to or cannot access the medical system, and hence do not become tested. A user-friendly test must be capable of being quickly performed by individuals who have no formal training, and it should require few steps and allow testing in any location at anytime chosen by the user.
In recent years, user-friendly diagnostic tests have been developed that allow individuals to detect analytes in undiluted fluid samples. Examples are pregnancy tests that individuals may purchase in any large supermarket and perform on undiluted urine at any location and at any time that they choose. Patents by Ullman et al., U.S. Pat. No. 4,857,453, issued Aug. 15, 1989; Nazareth et al., U.S. Pat. No. 5,739,041, issued Apr. 14, 1998, and Pawlak et al., U.S. Pat. No. 5,770,460 issued Jun. 23, 1998, are examples of urine HCG tests for pregnancy. Widely available tests for detecting serum glucose may be easily performed .by individuals, but they still require instrumentation. Tests requiring instrumentation are more expensive and do not fit our strict definition of being user-friendly.
Some analytes may be detected in undiluted whole blood, serum or plasma. U.S. Pat. No. 5,762,871, by Neyer, issued Mar. 10, 1998, and U.S. Pat. No. 6,027,692 by Galen et al., issued Feb. 22, 2000, teach tests of undiluted blood serum or plasma for glucose and fructosamine. U.S. Pat. No. 5,166,051 by Killeen et al., issued Nov. 24, 1992, instructs regarding tests of whole blood for analyzing serum cholesterol.
For other tests and assay formulations, detection is more accurate only after dilution of the test liquid. An example is the test for antibodies to HIV. Commercially available immunoassays, as well as rapid strip format tests for HIV antibody, routinely dilute the sample approximately 1:100 before testing, as shown in U.S. Pat. No. 5,922,533 by Vallari et al., issued Jul. 13, 1999. In these tests a uniform dilution. of serum is prepared in a separate location, and the test is then conducted with the uniformly diluted serum.
Attempts to dilute plasma or serum within the test device have employed washing the plasma or serum from a plasma separator/collector pad. An example is that taught by Bernstein et al., U.S. Pat. No. 5,753,497. The resulting dilutions are variable depending upon the volumes of wash fluid added. In addition, the dilutions are not uniform and result in gradient concentrations of serum components migrating down the test strip. The initial eluents from the collector pad contain high concentrations of plasma or serum relative to diluent, and later eluents contain small amounts since most of the plasma or serum has already been washed from the collector pad. This may produce undesirable effects on test performance, such as inconsistent migration rates down the test strip, or inadequate completion of reactivity between test labeling reagents and plasma or serum components that are present in high concentrations, such as immunoglobulin. This results in variations in the time required to complete the test and in some instances adverse effects on sensitivity or specificity.
Individuals conducting a test at home, or staff in a physician's office or point of care location, cannot easily separate plasma or serum from whole blood. They also cannot safely use pipettes to produce a reliable dilution for testing. Persons conducting the test also will not usually have available to them instrumentation for evaluating test strip results.
It would be useful to have a method and device that permits individuals to separate plasma or serum from finger-stick whole blood and obtain a reliable and relatively uniform dilution of that serum or plasma for testing. It would further be useful for the device design to allow migration of the diluted liquid sample along diagnostic test strips contained within the device, so that a diagnostic test result is rapidly produced. Optimally, the test device must provide a clear result that is easily interpreted by visual observation without instrumentation. Finally, to be widely accepted for testing anywhere and at anytime, the device and method must provide these results with a minimum number of easily performed steps and provide the diagnostic test result within approximately ten minutes.
A method and device that would permit reliable dilution of a sample liquid, and rapid determination of the presence or absence of specific analytes within that diluted sample, without requirements of formal training or instruments, would be very useful worldwide. The method and device of this invention seek to fulfill this need.